: The long-term objective of this proposal is to formulate precise, quantitative models for the perception of tones, noise, and speech in both normal and impaired hearing. Such models may aid in providing better diagnostic tools for hearing impairment and better rehabilitation of hearing-impaired listeners. The proposed project aims to investigate dynamic processes in the auditory system that affect the perception of loudness and roughness and to continue modeling of these processes. Model predictions will be compared to psychoacoustic data obtained in forced-choice experiments with cochlearly impaired listeners and with normal listeners tested in the quiet and with continuous maskers that are spectrally shaped to produce thresholds equal to those of an impaired listener. The specific aims encompass four areas. Specific aim 1 is to test several hypotheses related to the loudness ratio between equal-SPL long and short sounds. Binaural loudness summation for long and short tones will be measured as a function of level. A novel paradigm will be used to determine how loudness grows with stimulus duration by measuring the difference in duration required to produce equal loudness between equal-SPL monotic and diotic tones and between pure tones and tone and tone complexes. Specific aim 2 tests the hypotheses that intense 'recalibration' tones reduce the slope of normal listeners* loudness function for subsequent test tones at moderate levels and that recalibration is reduced or absent in impaired listeners, because it is mediated by efferent action on the outer hair cells. Loudness matches between tones at different frequencies will be obtained as a function of level with and without prior presentation of 85-dB-SPL recalibration tones. The effect of recalibration on temporal integration of loudness also will be examined. Specific aim 3 is to test the hypothesis that the form of the loudness function for a tone at low and moderate levels is approximately proportional to the square of the maximal basilar-membrane vibration amplitude. Growth of forward masking with on- and off-frequency maskers will be compared to loudness functions derived from measurements of binaural loudness summation and from measurements of temporal integration of loudness. Specific aim 4 is to test the hypothesis that loudness recalibration reduces roughness at moderate levels. Across-frequency roughness matches will be obtained as a function of level with and without recalibration.